Contributions of biomass/biofuel burning to organic aerosols and particulate matter in Tanzania, East Africa, based on analyses of ionic species, organic and elemental carbon, levoglucosan and mannosan

摘要

Atmospheric aerosol samples of PM and PM were collected at arural site in Tanzania, East Africa, in 2011 during wet and dry seasons andwere analysed for carbonaceous components, levoglucosan, mannosan andwater-soluble inorganic ions. The contributions of biomass/biofuel burningto the organic carbon (OC) and particulate matter (PM) mass were estimatedto be 46–52% and 87–13%, respectively. The mean mass concentrations ofPM and PM were 28 ± 6 μg m and 47 ± 8 μg min wet season, and 39 ± 10 μg m and61 ± 19 μg m in dry season, respectively. Total carbon (TC)accounted for 16–19% of the PM mass and 13–15% of thePM mass. On average, 86 to 89% of TC in PM and 87 to90% of TC in PM was OC, of which 67–72% and 63% was found tobe water-soluble organic carbon (WSOC) in PM and PM,respectively. We found that concentrations of levoglucosan and mannosan(specific organic tracers of pyrolysis of cellulose) well correlated withnon-sea-salt potassium (nss-K) ( = 0.56–0.75), OC( = 0.75–0.96) and WSOC ( = 0.52–0.78). The K / OCratios varied from 0.06 to 0.36 in PM and from 0.03 to 0.36 inPM with slightly higher ratios in dry season. Mean percent ratios oflevoglucosan and mannosan to OC were found to be 3–4% for PM andPM in both seasons. We found lower levoglucosan / K ratios andhigher K / EC (elemental carbon) ratios in the biomass-burning aerosols from Tanzania thanthose reported from other regions. This feature is consistent with the highlevels of potassium reported in the soils of Morogoro, Tanzania, suggestingan importance of direct emission of potassium by soil resuspension althoughK is present mostly in fine particles. It is also likely that biomassburning of vegetation of Tanzania emits high levels of potassium that maybe enriched in plant tissues. The present study demonstrates that emissionsfrom mixed biomass- and biofuel-burning activities largely influence the airquality in Tanzania.